In the oil and gas industry, wellhead topside pressure may exceed a maximum allowed pressure within production fluid pipelines downstream of the wellhead due to degraded pipe wall thickness or cost limitations that prevent the installation of full-rated piping. It is therefore necessary that such pipelines be protected against excessive pressure that might rupture the pipe, which would cause environmental pollution and be very expensive to replace. A conventional system used to protect pipelines from over-pressure is the high integrity protection system (HIPS). This is typically an electro-hydraulic system employing pressure sensors to measure the pressure in the pipes which are used through the electronics of a control module to control the closure of a production pipe HIPS valve. This arrangement retains the high pressure within a short section of pipeline between the production tree and the HIPS valve which is capable of withstanding the pressure. This prevents the main, thinner-walled section of the pipeline from being exposed to pressure levels which may exceed the pipeline's pressure rating.
It is a necessary requirement that the safety of the HIPS be tested regularly since a malfunction in operation of the HIPS presents the risk of significant damage to the pipeline. The conventional system cannot be tested during its operation. Thus, the production system has to cease operations and be isolated for the test. The interruption of operations has serious financial implications. In addition, at least one operator has to be close to the HIPS during the test, since operations of valves and other components are performed by people manually.
Various approaches have been proposed for testing and protecting valves and pipeline systems from overpressure. For example, published application US2005/0199286 discloses a high integrity pressure protection system in which two modules connected to two downstream pipelines and two upstream pipelines have inlet and outlet ports. A conduit circuit connects the two ports and a docking manifold is installed in the pipeline between upstream and downstream portions. The docking manifold selectively routes flows in each of the first and second pipelines through the first or second module. The system permits routing of flows from upstream regions of both of the pipelines through one of the modules and then to a downstream region of one of the pipelines to permit the other module to be removed for maintenance, repair and/or replacement. There is no disclosure or suggestion of an apparatus or method for testing the operation of the system while it is in operation.
For example, U.S. Pat. No. 6,591,201 to Hyde discloses a fluid energy pulse test system in which energy pulses are utilized to test dynamic performance characteristics of fluid control devices and systems, like gas-lift valves. This test system is useful for testing surface safety valves in hydraulic circuits, but does not provide safety information of the overall system's ability to perform safety function.
U.S. Pat. No. 6,880,567 to Klayer, et al. discloses a system that includes sensors, a safety control system and shut off valves used for protecting downstream process equipment from overpressure. This system utilizes a partial-stroke testing method in which block valves are closed until a predetermined point and then reopened. This system, however, has to interrupt production for the diagnostic testing.
U.S. Pat. No. 7,044,156 to Webster discloses a pipeline protection system in which pressure of fluid in a section of pipeline that exceeds a reference pressure of the hydraulic fluid supplied to a differential pressure valve, the differential pressure valve is opened, and thereby causes the hydraulic pressure in the hydraulically actuated valve to be released via a vent. The protection system, however, does not provide any valve diagnostic means and is forced to interrupt the production for shut off valves to be fully closed.
U.S. Pat. No. 5,524,484 to Sullivan discloses a solenoid-operated valve diagnostic system which permits the valve user with the ability to monitor the condition of the valve in service over time to detect any degradation or problems in the valve and its components and correct them before a failure of the valve occurs. This system does not permit a testing of shut off valves without an interruption of production.
U.S. Pat. No. 4,903,529 to Hodge discloses a method for testing a hydraulic fluid system in which a portable analyzing apparatus has a supply of hydraulic fluid, an outlet conduit, a unit for supplying hydraulic fluid under pressure from the supply to the outlet conduit, a return conduit communicating with the supply, a fluid pressure monitor connected to the outlet conduit, and a fluid flow monitor in the return conduit. The analyzing apparatus disconnects the fluid inlet of the device from the source and connects the fluid inlet to the outlet conduit, and disconnects the fluid outlet of the device from the reservoir and connects that fluid outlet to the return conduit. Fluid pressure is monitored in the outlet conduit and the flow of fluid through the return conduit with the unit in place in the system. This method, however, requires that the production be interrupted for the testing of the hydraulic system.
U.S. Pat. No. 4,174,829 to Roark, et al. discloses a pressure sensing safety device in which a transducer produces an electrical signal in proportion to a sensed pressure and a pilot device indicates a sensing out-of-range pressure when the sensed pressure exceeds a predetermined range, which permits an appropriate remedial action to be taken if necessary. The device requires operators intervention.
U.S. Pat. No. 4,215,746 to Hallden, et al. discloses a pressure responsive safety system for fluid lines which shuts in a well in the event of unusual pressure conditions in the production line of the well. Once the safety valve has closed, a controller for detecting when the pressure is within a predetermined range is latched out of service and must be manually reset before the safety valve can be opened. The system results in an interruption of production and operators intervention.
An additional limitation of existing testing and protection systems relates to diagnostic procedures. Existing technology relies on process simulations and system performance verification procedures conducted once during system design and commissioning to set the trip point for the protection system. However, this procedure does not take into account the fact that process dynamics and valve stroke time can change with the passage of time.
It is therefore an object of the present invention to provide an apparatus and a method for testing the HIPS while it is in operation while the HIPS operates as a flowline to a piping system and without shutting down the production line to which it is connected.
Another object is to provide an apparatus and a method for automatically testing the safety of a HIPS without the intervention of an operator.
It is an additional object of the present invention to perform measurements at each system demand and verify that the HIPS response time remains within an appropriate range based upon those measurements, rather than based upon historic start-up data.